Network In-Line Tester

1. A network in-line tester for testing a telecommunications network, the tester configured for connection in line in a communications channel in the network so that all packets within that channel have to flow through the tester, wherein the tester is adapted to perform at least one operation on at least one selected packet flow as it flows through the tester, wherein said tester comprises one or more processors and/or circuits configured to: vary the selected packet flow by replaying at least one characteristic or profile recorded from a real communication signal in a different flow on the selected packet flow as the selected packet flow flows through the tester to replicate the characteristics of interest on the selected packet flow, wherein the at least one recorded characteristic or profile comprises a delay characteristic or delay profile and varying the selected packet flow by said tester involves varying relative timings of packets in the packet flow using the recorded delay characteristic or profile thereby simulating real-world time delay effects on the telecommunications network; output the varied selected packet flow via an output of the tester into the communication channel.

2. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is configured to identify and label individual packets or sequences of packets in the packet flow.

3. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is configured to select at least one packet or packet flow depending on at least one pre-determined criteria.

4. A tester as claimed in claim 3 wherein at least one pre-determined criteria is user selected.

5. A tester as claimed in claim 3 wherein the at least one pre-determined criteria is a sub-segment of each packet.

6. A tester as claimed in claim 5 wherein the sub-segment is a portion of the packet header.

7. A tester as claimed in claim 1 wherein the characteristic or profile is recorded from a real communication signal in a different flow in a different geographic location.

8. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is configured to modify the recorded characteristic or profile.

9. A tester as claimed in claim 1 , wherein the at least one operation includes at least one of: injecting errors into packets; varying a delay experienced by a packet as it passes through the tester; injecting a delay profile into the packet flow; changing bits within the packets to communicate an alarm state; changing management and/or traffic packets in selected flows to appear to be associated with other flows.

10. A tester as claimed in claim 9 , wherein one or more processors and/or circuits is configured to inject a delay profile into the packet flow under test concurrently with injecting error events.

11. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is configured for time stamping each packet as it arrives.

12. A tester as claimed in claim 11 wherein the timestamp remains with the packet as it passes through the tester.

13. A tester as claimed in claim 11 , wherein one or more processors and/or circuits is operable to use the timestamp to reconstruct at least one packet at an output to be identical to the received packet.

14. A tester as claimed in claim 11 , wherein one or more processors and/or circuits is operable to use the timestamp to change the timing of at least one of the packets.

15. A tester as claimed in claim 14 , wherein one or more processors and/or circuits is adapted to change the timing by doing at least one of re-ordering the packets and changing the time-gap between packets.

16. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is adapted to allow one or more packets or flows to pass through it unaffected.

17. A tester as claimed in claim 1 comprising means for storing selected characteristics of selected packet flows.

18. A tester as claimed in claim 1 , wherein one or more processors and/or circuits is adapted to test packet flow in two directions.

19. A tester as claimed claim 1 comprising a clock that is synchronised with a clock in a network transmit source.

20. A test system comprising a plurality of testers as claimed in claim 1 .

21. A test system as claimed in claim 20 comprising means for passing information between the testers.

22. A test system as claimed in claim 20 , wherein one of the testers is configured to change a packet flow and another is configured to monitor the impact of the changes made.

23. A test system as claimed in claim 20 comprising means for collecting information from a plurality of the testers.

24. A test system as claimed in claim 20 comprising one or more processors and/or circuits adapted to replay of one or more stored characteristics of one or more packet flows on one or more packet flows in a tester.

25. A test system as claimed in claim 24 wherein the stored characteristic is a recorded version of one or more real packet flows.

26. A test system as claimed in claim 20 comprising one or more processors and/or circuits adapted to monitor or evaluate the impact of an action in one tester on one or more packets or sequences of packets in a downstream tester.